Location tracking devices and other such mobile terminals typically comprise satellite-based location determination functionality, e.g. a receiver for global positioning system (GPS) or GLONASS (Global Navigation Satellite System) and to some extent cellular communication functionality, e.g. transceiver for collecting cell data from nearby cells/base stations and reporting it to a receiver at the remote location. To determine a location, a GPS receiver must have current almanac data and ephemeris data for at least three appropriate satellites and the receiver must have an initial estimate of its location. However, the reception of signals from the satellites easily suffer from interruptions caused by landscape obstructions such as geographic features, buildings, trees, etc. Because location tracking devices are often operated in environments, such as cities and urban areas, wherein GPS signal reception will be intermittent, this can result in poor performance of the location tracking system.
Documents WO 2008/080226, US 2008/0171557, EP 1548456 and U.S. Pat. No. 7,215,967 address the weaknesses of GPS-based location tracking devices and other such mobile terminals and propose assisted GPS (AGPS) to update the almanac and/or ephemeris data in order to improve performance of such devices. AGPS systems exploit remote terrestrial stations in locations in which good reception of satellite signals is expected and assistance data based on received signals are then transmitted e.g. via a cellular communication network to the mobile terminals. The start-up of the GPS-receiver typically requires the initial estimate of its location and this process takes several minutes (so called cold start time). In order to speed up the start-up of the GPS-receiver the cited documents present that the remote/mobile terrestrial stations produce assistance data based on identifiers of cellular network base stations and time delay data received from the cellular network base stations, and this data is used to improve the initial location position estimate. Time delay data which is available from the base station is used to estimate the distance between the location tracking device and the base station. To determine location estimates from the base station delay data, it is necessary to know the location of the base stations which is not always axiomatic due to security or other reasons. Finally, the location tracking device determines its location using the initial location estimation based on assistance data including identifiers, time delay data and valid GPS ephemeris data which it obtained from the remote terrestrial station. In the prior art systems the initial, actual and final location determination always requires reception of the satellite-based positioning data in each phase which is time consuming task.
The location estimation procedures described above take into account assistance data that includes ephemeris data received from satellites and identifier and time delay data from the cellular base stations. This easily results inaccurate location estimation because certain environment obstructions and their influences are ignored. The location estimation described above is based on performing an analysis of the location of the mobile terminal with respect to the locations of the base station and therefore if the exact base station locations are not available the resulting location estimation becomes distorted. The location estimation procedures described above do not estimate for each cell a location of a base station or a coverage area of the base station (area reached by the radio signal). The location estimation procedures described above don't make any estimation of a type of the cell with regard to landscape and cityscape, etc.